A semiconductor device in this specification refers to any device that can function by utilizing semiconductor characteristics; electro-optic devices, semiconductor circuits, and electronic appliances are all semiconductor devices.
In recent years, a semiconductor device having a sensing element for detecting light (also called a “photosensor”) has drawn attention. As examples of the semiconductor device having a photosensor, a CCD image sensor, a CMOS image sensor, and the like can be given. They are used in electronic appliances equipped with an image pick-up function such as a digital still camera and a mobile phone.
A semiconductor device having a photosensor in a display region, which can detect a touch of an object (e.g., a pencil, a finger) on the display region, is also called a touch panel, a touch screen, or the like (hereinafter simply called a “touch panel”). Such a photosensor provided in the display region of the semiconductor device enables the display region to double as an input region; as an example, a semiconductor device equipped with an image loading function has been disclosed in Patent Document 1.